FHWA Scenario Planning Guidebook

Phase 5. What Impacts Will Scenarios Have?

Assess scenario impacts, influences, and effects.

Phase 5 focuses on analyzing scenarios. Scenario analysis typically involves assessing the impacts, influences, and effects that various scenarios exert on selected indicators. As described in Phase 3, indicators are statistical values (e.g., level of employment) or groups of values that are used to compare two or more scenarios. While Phase 5 focuses on scenario analysis through use of indicators, these indicators might have already been developed or considered in earlier phases, particularly Phase 4.

When analyzing scenarios, agencies can consider either a qualitative or a quantitative approach. Using a qualitative approach, agencies could utilize working groups or roundtables to facilitate discussion and brainstorming about scenario impacts. Agencies considering a quantitative approach could use the travel demand model or a GIS-based scenario analysis tool.

Each step is listed below, along with associated key questions that agencies can consider. Some steps provide examples of additional issues or questions for further consideration.

Step 5.1: Develop or identify indicators to compare scenarios.

Develop indicators that are discrete, measurable, and describable. Indicators should be developed for qualitative or quantitative data, depending on what information is available. Indicator development might proceed in tandem with refinement of scenario analysis tools or the travel demand model. Indicators might have already been developed or considered in earlier phases, particularly Phase 4.

Use agreed-upon goals, values, and/or objectives to guide development of scenario indicators and build on the set of working principles that is the possible outcome of Phase 3.

Use qualitative methods to compare scenarios against indicators that cannot be modeled or for which there are few data. For example, as part of its scenario planning effort, TJPDC assembled a panel of local residents with professional expertise in water resources. The panel provided a qualitative evaluation of the water-use impacts of alternative scenarios.

Consider the tradeoffs involved with determining the appropriate number and complexity of indicators. More indicators might require more time and data but could provide a more comprehensive scenario assessment. However, fewer indicators could allow a more focused or targeted analysis.

Consider that successful indicators highlight the key aspects of scenario outcomes. They also provide an accurate understanding of impacts as they relate to the values, goals, and aspirations established by stakeholders in Phase 3.

Developing Scenario Indicators

A variety of applications and models can be used to help identify and develop indicators:

The travel demand model can be used to gauge transportation accessibility.

GIS-based applications can be used to assess sidewalk availability, buffer areas for transit ridership, or other impacts.

The Environmental Protection Agency's Motor Vehicle Emissions Simulator (MOVES) model can be used to assess air quality or greenhouse gas emissions.

Examples of indicators used in previous scenario planning efforts are listed below.

Environmental/land-use indicators

Acres of non-urbanized land

Percentage of farms and forests

Community livability indicators

Percentage of population living in clustered communities

Percentage of population with access to transit

Annual gallons of gas consumed

Jobs/housing indicators

Number and/or percentage of jobs located near affordable housing

Change in average commuting times

Transportation system indicators

Number of highway congested hours

Vehicle miles traveled by mode

Percentage of work or all trips by mode

Climate change indicators

Greenhouse gas emissions by sector and county

Greenhouse gas emissions due to vehicle miles traveled

Acres of land deforested for development

Step 5.2: Use indicators to identify scenario impacts.

Use chosen analysis tools and/or the travel demand model to assess each scenario.

Translate each scenario into terms that are appropriate for the analysis tool or travel demand model. For example, changes to development policies must be translated into assumed impacts on growth in each analysis unit (e.g., transportation analysis zone). Similarly, any future changes that are expected to affect travel behavior, such as aging populations, must be reflected in the model or analysis tool.

To analyze scenario impacts with the chosen indicators, compile outputs from the qualitative analysis, travel demand model, or analysis tool.

Consider development of documents, such as brochures or fliers, to describe scenario performance.

If needed, refine scenarios and indicators on the basis of stakeholder feedback. Scenario analysis can be repeated with a narrower set of indicators.

Developing a Matrix for Scenario Analysis

TJPDC used a matrix to illustrate scenario performance.* The matrix compared scenario outputs with general as well as specific indicators developed from the Sustainability Accords principles.

The matrix, shown below, includes analysis of each of the four scenarios (dispersed, town centers, CoreL, and CoreM) developed by TJPDC. The italicized figures under the dispersed scenario column indicate that this scenario scored lowest on every measure compared with other scenarios. The low scores indicate the public's growth preferences in rejecting a dispersed, low-density pattern in favor of clustered, enhanced communities along major corridors and key crossroads.

The numbers under the scenario columns show the comparison of each scenario's land-use and transportation networks with the measures in the left-hand column. For example, only 55 percent of land cover in the dispersed scenario was composed of farms and forests.

Phase 5 Outputs

Phase 5 has several possible outputs, including a list of indicators to compare scenario outcomes and a qualitative or quantitative assessment of scenario impacts. Some agencies have used tables or matrices to outline how scenarios perform against the chosen indicators. Other agencies utilizing a qualitative scenario assessment approach have summarized scenario performance in white papers or other documents, or through discussion in focus groups, roundtables, or expert panels.